This invention relates to an operational control system for an engine and more particularly to an improved temperature responsive arrangement for controlling an engine and particularly its ignition system.
There are many instances in the control of an engine wherein the engine operating temperature is one of the control parameters. For example, it has been proposed to control the idle speed of an engine in response to temperature so that the engine will be set to run faster at low engine temperatures than once the engine warms up. One way in which this speed increase is accomplished, is by advancing the timing of the spark firing when engine temperatures are low.
It has been the practice to position a temperature sensor in a portion of the engine so as to sense its temperature and provide an output signal indicative of actual temperature. Such temperature sensors may be mounted in either the cylinder block or cylinder head of the engine and generally project into the engine cooling jacket, if the engine is liquid cooled, so as to provide an accurate indication of temperature. Although this method of temperature sensing is quite accurate and representative of actual engine temperature, there are some disadvantages with this type of arrangement.
In many engine applications it is very difficult to provide the space required for the temperature sensor, particularly if the temperature sensor is to be mounted in a location where it will provide an accurate indication of temperature. In addition, if the temperature sensor provides a signal for controlling the ignition system, the length of the wires leading from the temperature sensor to the ignition system and the attendant electrical connections can give rise to problems in insuring that an adequate and correct signal is transmitted.
It has, therefore, been proposed to provide a temperature sensor that is mounted directly in the ignition circuit with the ignition circuit being mounted on the engine so as to provide temperature control and the existence of a temperature that is related to the engine temperature at the temperature sensor. This type of arrangement avoids the disadvantages as aforenoted, but itself has certain problems.
Although the mounting of the temperature sensor in the ignition circuit has the advantages aforenoted, the temperature sensor actually provides an accurate indication of engine temperature only when the engine and ignition circuit have both cooled to ambient temperature. If, however, the engine has been running for a period of time and then is shut off, the temperature sensor will cool more rapidly than the engine due to its greater mass and internal heat. Thus, if the engine is restarted after a short delay, the temperature sensor will sense a lower temperature than the actual engine temperature and the control will be inaccurate. When the temperature sensor is used to provide an increase in engine speed and/or spark advance for faster cold warm up, this will mean that the engine, which is at or close to its operating temperature, will be run at too high a rate of speed and at too much spark advance.
It is, therefore, a principal object to this invention to provide an improved arrangement for providing running control for an engine.
It is a further object to this invention to provide an improved temperature sensing device and control system for an internal combustion engine.
It is a yet further object to this invention to provide an improved and simplified arrangement for controlling an engine in response to temperature that will be accurate under all conditions.